The family of David Hartley visit at Falcon Lake Wednesday. Hartley's wife, Tiffany, says he was shot and killed by Mexican pirates as the couple was jet skiing on the Mexican side of the lake last week.

In part fueled by the improbability of the phrase "Mexican pirates" and given past crimes where innocent-seeming spouses eventually faced murder charges, doubts about Ms. Hartley's story have bubbled up on cable TV shows, Twitter, and even along the 60-mile-long border lake where the shooting allegedly happened.

"There are a whole lot of doubts. Very few believe it. [The story] is just too wild with too many loopholes," says John Williams, a resident of Zapata, Texas, and a fishing guide on Falcon Lake since 1964, in a phone interview. "I don’t know what happened. They could have taken him off into desert, and he'll never be seen again, but I don't think anybody will ever know unless they come up and tell you."

The lake, long known as a crossing point for illicit cross-border activity, has lately become a hideout for cartels fleeing a Mexican government crackdown. The Gulf Coast Cartel and its former enforcers, the Zetas, are fighting for control of the lake. This year, cartel-linked pirates have reportedly robbed or attempted to rob US bass fishermen on five different occasions, though Mr. Hartley is the first reported death.

Ms. Hartley has said her husband was shot by men in a boat after she and her husband drove their jet skis to the Mexican side of the lake. The men in the boat then chased her back to the US side, she said.

Texas state legislator Aaron Pena, who accompanied Ms. Hartley to the rose-laying ceremony on the lake Wednesday, believes the pirates were likely junior cartel members looking to steal the couple's jet skis, and they carried off the watercraft and Mr. Hartley's body after the shooting.

But that scenario seems too convenient for some commentators.

"It certainly feels better to imagine that a young good-looking married couple was blissfully in love, and that they were simply having fun in the sun when dark forces struck," writes law professor Wendy Murphy, author of "And Justice for Some," in a Fox News commentary. "But let's remember the Scott Peterson and Charles Stuart cases. Two men seemingly head over heels in love with their beautiful pregnant wives when they claimed an unknown killer ruined their picture-perfect lives."

In Zapata, some locals pointed out that jet skiers are unusual on a lake frequented mostly by fishermen, and that it's very rare to see jet skiers cross onto the Mexican side of the lake, which is marked by concrete posts. The Hartleys have lived in Mexico and had few reservations about crossing into Mexico to visit at a half-submerged church near Old Guerrero, despite warnings about pirates, Ms. Hartley has explained

Earlier this week, however, the district attorney of bordering Tamaulipas State, Marco Antonio Guerrero Carrixales, told the McAllen Monitor that he's not "certain that the incident happened the way they are telling us."

Mexican officials say no one on their side reported hearing the sound of gun shots or even a jet ski on the lake. Nevertheless, Mexican authorities stepped up the search for Hartley on the Mexican side of the lake on Wednesday.

For their part, US authorities have come strongly to Ms. Hartley's defense. At least one eyewitness saw Ms. Hartley fleeing back into US waters pursued by an Argos-style boat that the local cartels are known to possess, authorities said.

Texas state lawmaker Mr. Pena said the conspiracy theories only play into the Mexican state authorities' inability to find Mr. Hartley's body – or identify the possible cartel members who carried out the shooting.

Blaming Ms. Hartley "is a convenient excuse for the sorry response [by Mexico]," says Pena. "Everything tells me that she's being truthful. There was a witness, its fits with other criminal activity seen in the area, and how do you make assumptions without having evidence, and the only evidence is what she's saying."

In a TV interview on Wednesday, Ms. Hartley, who has appealed to President Obama to help her find her husband's body, acknowledged the questions around what happened last Thursday afternoon on the deceptively placid border lake.

"It's just hard to hear" the conspiracy theories, she said. "But I can see it from their point of view. I can understand why they might think that, but it's not true. I would never even think of hurting my husband. I loved him."